1. Field of Invention
This invention relates generally to optical filters and shutters for protecting optical devices from excessive energy levels, and more particularly to optical devices reactive to excessive energy levels such that the device transforms from a transmissive device to a blocking device at energy levels above its threshold.
2. Brief Description of the Prior Art
Many applications utilize high energy laser beams such as laser range finding and laser tracking. The detectors used to receive the laser beams need to be protected so as to insure that they will not be destroyed by a blast of laser energy which is above the detector's maximum allowable exposure.
Previously, protective devices utilized optical modulators such as Pockels Cells whose polarization would vary according to the surrounding magnetic field. Also, mechanical shutter systems have been developed which convert a triggering signal into a voltage which drives a piston to close the shutter so as to protect the equipment from being damaged. A mechanical system such as this is disclosed in U.S. Pat. No. 4,515,173 issued to Eugene L. Zimmerman, on May 7, 1985. Such systems had the disadvantages of being either too slow to protect modern sensing devices from high energy sources of light, or too large to be effectively utilized with the sensor. Additionally, some of the systems were only able to be used once since they were functionally destroyed in protecting the sensor.
It is the object of this invention to provide an optical shutter that is optically clear at the sensor frequency, reactive to high energy light sources so as to protect sensors quickly enoughto prevent damage, and completely reusable.